LONDON - Britons voted on Thursday in a referendum on electoral reform that has split the year-old coalition government and raised doubts about whether the partnership will last.

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Voters across much of England are electing local councillors, while elections will also be held for devolved assemblies in Scotland, Northern Ireland and Wales.

Polls opened at 0600 GMT, and first results will emerge shortly after they close at 2100 GMT, although the outcome of the referendum is not due until late on Friday evening.

The coalition government, led by the Conservatives in alliance with the smaller Liberal Democrats, is expected to suffer a backlash from voters unhappy about tough austerity measures designed to tame a record peacetime budget deficit.

However, the referendum on whether to change the way members of parliament are elected has been the real source of tension between the coalition partners, who are on opposite sides of the argument and have traded insults during the campaign.

Voters are expected to reject change in favour of sticking with the long-established, first-past-the-post system, disappointing the Lib Dems.

Analysts believe the coalition, Britain's first since World War II, will stick together because for either partner to force an early election would risk political suicide at a time when the economy is growing very slowly.

"I think they still need each other and will try to make this work," said Tim Bale, politics professor at the University of Sussex in southern England. "The atmosphere has changed but the parliamentary arithmetic has not."

Financial markets want a stable government to see through a five-year plan virtually to eliminate by 2015 a budget deficit that had been running at more than 10 percent of national output.